Light-emitting element driving device, light-emitting device, and vehicle

ABSTRACT

A light emitting drive device has an output voltage supply unit, and an emergency drive unit. The output voltage supply unit generates an output voltage from an input voltage on the basis of a control signal transmitted from a control unit, and supplies at least one light emitting element with the output voltage. In the cases where the emergency drive unit received a signal indicating abnormality of the control unit, the emergency drive unit lights the whole or a part of the at least one light emitting element irrespective of the control signal transmitted from the control unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/512,341, filed Mar. 17, 2017 which is a 371 U.S. National phaseapplication for PCT/JP2015/075025 filed Sep. 3, 2015, which claimspriority under 35 U.S.C. § 119(a) on Japanese Patent Application No.2014-204261 filed on Oct. 2, 2014, the entire contents of which arehereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a light-emitting element driving devicefor driving a light-emitting element, and to a light-emitting device anda vehicle that employ a light-emitting element driving device.

BACKGROUND ART

FIG. 16 is a diagram showing one example of a light-emitting device. Thelight-emitting device of this example includes at least onelight-emitting element (in FIG. 16, light-emitting diodes) Z1, alight-emitting element driver IC (integrated circuit) 100 which drivesthe light-emitting element Z1, a P-channel MOS(metal-oxide-semiconductor) transistor P1 which is inserted in the powerfeed path from the light-emitting element driver IC 100 to thelight-emitting element Z1, a controller IC 200 which feeds thelight-emitting element driver IC 100 with a PWM (pulse-width modulation)dimming signal S1, and a monitor IC 300 which checks for a fault in thecontroller IC 200.

The light-emitting element driver IC 100 is a semiconductor integratedcircuit device that has integrated into it an output voltage generator101, which generates a constant output voltage Vo from an input voltageVi to feed the output voltage Vo to the light-emitting element Z1, andan output current controller 102, which turns the transistor P1 ON andOFF according to the PWM dimming signal S1 output from the controller IC200 to control the duty of an output current Io through thelight-emitting element Z1 (thereby to control the luminance of thelight-emitting element Z1). To increase the luminance of thelight-emitting element Z1, the ON duty of the PWM dimming signal S1 (theproportion of the ON period Ton in the period T shown in FIG. 17) is setat a larger value; reversely, to decrease the luminance of thelight-emitting element Z1, the ON duty of the PWM dimming signal S1 isset at a smaller value. The light-emitting element driver IC 100 alsohas external terminals T11 to T14. To the external terminal T11, theinput voltage Vi is applied. From the external terminal T12, the outputvoltage Vo is output. To the external terminal T13, the PWM dimmingsignal S1 is fed. From the external terminal T14, a gate control signalfor turning the transistor P1 ON and OFF is output.

The controller IC 200 is a semiconductor integrated circuit device thathas integrated into it a clock circuit 201, which generates a clocksignal S2, and a PWM circuit 202, which generates the PWM dimming signalS1 based on the clock signal S2. The controller IC 200 also has externalterminals T21 to T23. From the external terminal T21, the PWM dimmingsignal S1 is output. From the external terminal T22, the clock signal S2is output. To the external terminal T23, the monitoring result signal S3is fed. There is no particular restriction on how the controller IC 200uses the monitoring result signal S3; for example, in one conceivableconfiguration, when the monitoring result signal S3 is in a state thatindicates a fault in the controller IC 200, the operation of thecontroller IC 200 can be stopped completely for increased safety.

The monitor IC 300 has external terminals T31 and T32. Based on theclock signal S2 fed to the external terminal T31, the monitor IC 300checks whether or not the controller IC 200 is faulty to output thecheck result, as the monitoring result signal S3, from the externalterminal T32. In this example, when the controller IC 200 is not faulty,the monitoring result signal S3 is at HIGH level, and when thecontroller IC 200 is faulty, the monitoring result signal S3 is at LOWlevel. That is, a LOW-level monitoring result signal S3 serves as asignal that indicates a fault in the controller IC 200.

Although in FIG. 16 the monitoring result signal S3 is fed only to thecontroller IC 200, this is not meant as any limitation; for example,instead of the controller IC 200, or in addition to the controller IC200, a controller that controls the entire appliance that incorporatesthe light-emitting device shown in FIG. 16 may be fed with themonitoring result signal S3. Although in FIG. 16 the monitor IC 300checks for only a fault in the controller IC 200, a configuration isalso possible where the controller IC 200 and the monitor IC 300 eachcheck for a fault in the other.

LIST OF CITATIONS Patent Literature

Patent Document 1: Japanese Patent Application published as No.2013-217213Patent Document 2: Japanese Patent Application published as No.2007-218196

SUMMARY OF THE INVENTION Technical Problem

One conceivable application of the light-emitting device shown in FIG.16 is in lights mounted on vehicles.

It is preferable that vehicles be furnished with a limp-home capabilitythat enables them to move over a short distance to a safe place in casea failure prevents them from travelling normally. For example, PatentDocument 1 discloses a limp-home capability related to a common-railfuel injection control device in vehicles, and Patent Document 2discloses a limp-home capability related to a DPF (diesel particulatefilter) in vehicles.

Inconveniently, however, the light-emitting device shown in FIG. 16 hasthe following drawback. When a fault in the controller IC 200 causes theclock signal S2 to cease to be generated (after time point t1 in FIG.17), no pulses appear in the PWM dimming signal S1 any longer (seebroken lines in the PWM dimming signal S1 shown in FIG. 17); this makesthe ON duty of the PWM dimming signal S1 zero, and makes the outputcurrent Io zero. This means that it is impossible to furnish lights forvehicles that incorporate the light-emitting device shown in FIG. 16with a limp-home capability for night travel and the like.

Against the background discussed above, an object of the presentinvention is to provide a light-emitting element driving device thatoperates based on a control signal from a controller so long as thecontroller is operating normally but that turns ON a light-emittingelement irrespective of the control signal from the controller when thecontroller is operating abnormally, and another object of the presentinvention is to provide a light-emitting device and a vehicle thatemploy such a light-emitting element driving device.

Means for Solving the Problem

To achieve the above objects, according to one aspect of the presentinvention, a light-emitting element driving device includes: an outputvoltage feeder configured to generate an output voltage from an inputvoltage based on a control signal from a controller to feed the outputvoltage to at least one light-emitting element; and an emergency driverconfigured to turn ON all or part of the at least one light-emittingelement irrespective of the control signal from the controller onreceiving a signal indicating a fault in the controller. (A firstconfiguration.)

In the light-emitting element driving device of the first configurationdescribed above, preferably, the value of the current that the emergencydriver outputs to all or the part of the at least one light-emittingelement is smaller than the value of the current that the output voltagegenerator outputs to the at least one light-emitting element. (A secondconfiguration.)

In the light-emitting element driving device of the first or secondconfiguration described above, preferably, the output voltage generatorand the emergency driver share the following circuit blocks betweenthem: a high-side transistor and a low-side transistor connected betweena terminal to which the input voltage is applied and a ground terminal,the connection node between the high-side and low-side transistors beingconnected via a coil to the output capacitor; a high-side driver and alow-side driver configured to generate drive control signals for thehigh-side and low-side transistors respectively; an amplifier configuredto generate a feedback voltage commensurate with the current through theat least one light-emitting element; and a driver controller configuredto drive the high-side and low-side drivers so as to turn the high-sideand low-side transistors ON and OFF according to the feedback voltage.Here, the high-side and low-side transistors, the high-side and low-sidedrivers, the amplifier, and the driver controller are all integrated ina single semiconductor device. (A third configuration.)

In the light-emitting element driving device of the third configurationdescribed above, preferably, the emergency driver includes a selectorconfigured to select and output the control signal when no signalindicating a fault in the controller is received and to select andoutput a constant voltage when a signal indicating a fault in thecontroller is received. Here, the driver controller is configured toswitch whether or not to drive the high-side and low-side driversaccording to the output of the selector. (A fourth configuration.)

In the light-emitting element driving device of the fourth configurationdescribed above, preferably, the selector is integrated in the singlesemiconductor device. (A fifth configuration.)

According to another aspect of the present invention, a light-emittingdevice includes: a light-emitting element driving device of any one ofthe first to fifth configurations described above; at least onelight-emitting element configured to be driven by the light-emittingelement driving device; a controller configured to feed a control signalto the light-emitting element driving device; and a monitor configuredto monitor the controller to transmit, on detecting a fault in thecontroller, a signal indicating the fault in the controller to thelight-emitting element driving device. (A sixth configuration.)

In the light-emitting device of the sixth configuration described above,preferably, the light-emitting element is a light-emitting diode or anorganic EL element. (A seventh configuration.)

In the light-emitting device of the seventh configuration describedabove, preferably, the light-emitting device is used as avehicle-mounted lamp. (An eighth configuration.)

In the light-emitting device of the eighth configuration describedabove, preferably, the light-emitting device is mounted as a head lightmodule, a turn lamp module, or a rear lamp module on a vehicle. (A ninthconfiguration.)

According to yet another aspect of the present invention, a vehicleincludes a light-emitting device of the eighth or ninth configurationdescribed above. (A tenth configuration.)

In the vehicle of the tenth configuration described above, preferably,the light-emitting device is used as one of a head light, a light sourcefor daytime running light, a tail lamp, a stop lamp, and a turn lamp.(An eleventh configuration.)

Advantageous Effects of the Invention

According to the present invention, it is possible to provide alight-emitting element driving device that operates based on a controlsignal from a controller so long as the controller is operating normallybut that turns ON a light-emitting element irrespective of the controlsignal from the controller when the controller is operating abnormally,and to provide a light-emitting device and a vehicle that employ such alight-emitting element driving device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a light-emitting device according to a firstembodiment;

FIG. 2 is a timing chart illustrating an example of the operation of alight-emitting device according to the first or a third embodiment;

FIG. 3 is a diagram showing a light-emitting device according to asecond embodiment;

FIG. 4 is a timing chart illustrating an example of the operation of alight-emitting device according to the second or a fourth embodiment;

FIG. 5 is a diagram showing a light-emitting device according to thethird embodiment;

FIG. 6 is a diagram showing a light-emitting device according to thefourth embodiment;

FIG. 7 is a diagram showing a light-emitting device according to a fifthembodiment;

FIG. 8 is a timing chart illustrating an example of the operation of alight-emitting device according to the fifth embodiment;

FIG. 9 is a diagram showing a light-emitting device according to a sixthembodiment;

FIG. 10 is a timing chart illustrating an example of the operation of alight-emitting device according to the sixth embodiment;

FIG. 11 is an exterior view (front side) of a vehicle havinglight-emitting devices mounted on it;

FIG. 12 is an exterior view (rear side) of a vehicle havinglight-emitting devices mounted on it;

FIG. 13 is an exterior view of an LED head light module;

FIG. 14 is an exterior view of an LED turn lamp module;

FIG. 15 is an exterior view of an LED rear lamp module;

FIG. 16 is a diagram showing an example of a light-emitting device; and

FIG. 17 is a timing chart illustrating an example of the operation ofthe light-emitting device shown in FIG. 16.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 1 is a diagram showing a light-emitting device according to a firstembodiment. In FIG. 1, such parts as are found also in FIG. 16 areidentified by common reference numerals, and no detailed descriptionwill be repeated as to them.

The light-emitting device shown in FIG. 1 includes at least onelight-emitting element (in FIG. 1, light-emitting diodes) Z1, alight-emitting element driver IC 110 which drives the light-emittingelement Z1, a transistor P1 which is inserted in the power feed pathfrom the light-emitting element driver IC 110 to the light-emittingelement Z1, a controller IC 200 which feeds the light-emitting elementdriver IC 110 with a PWM dimming signal S1, and a monitor IC 300 whichchecks for a fault in the controller IC 200.

The light-emitting element driver IC 110, as compared with thelight-emitting element driver IC 100 shown in FIG. 16, additionallyincludes a switch SW1 and an external terminal T15. To the externalterminal T15, a monitoring result signal S3 is fed. The switch SW1operates according to the monitoring result signal S3 fed to theexternal terminal T15. Specifically, when the monitoring result signalS3 is at HIGH level, that is, when no signal indicating a fault in thecontroller IC 200 is received, the switch SW1 selects the PWM dimmingsignal S1 fed to the external terminal T13 to feed it to the outputcurrent controller 102. On the other hand, when the monitoring resultsignal S3 is at LOW level, that is, when a signal indicating a fault inthe controller IC 200 is received, the switch SW1 selects the terminalto which a constant voltage Vreg (a voltage corresponding to the HIGHlevel of the PWM dimming signal S1) is applied to feed it to the outputcurrent controller 102.

The output current controller 102 keeps the transistor P1 ON when fedwith a HIGH-level PWM dimming signal S1 from the switch SW1, keeps thetransistor P1 OFF when fed with a LOW-level PWM dimming signal S1 fromthe switch SW1, and keeps the transistor P1 ON when fed with theconstant voltage Vreg from the switch SW1. Thus, the output voltagegenerator 101, the output current controller 102, the transistor P1, andthe switch SW1 serve both as an output voltage feeder which generatesthe output voltage Vo from the input voltage Vi based on the PWM dimmingsignal S1 from the controller IC 200 to feed the output voltage Vo tothe light-emitting element Z1 and as an emergency driver which, onreceiving a signal indicating a fault in the controller IC 200, turnsthe light-emitting element Z1 ON irrespective of the PWM dimming signalS1 from the controller IC 200.

FIG. 2 is a timing chart illustrating an example of the operation of thelight-emitting device shown in FIG. 1, and depicts, from top down, theclock signal S2, the monitoring result signal S3, the PWM dimming signalS1, and the output current Io.

When a fault in the controller IC 200 causes the clock signal S2 tocease to be generated (after time point t1 in FIG. 2), no pulses appearin the PWM dimming signal S1 any longer (see broken lines in the PWMdimming signal S1 shown in FIG. 2), and the ON duty of the PWM dimmingsignal S1 becomes zero. However, when a fault in the controller IC 200causes the clock signal S2 to cease to be generated (after time point t1in FIG. 2), the monitoring result signal S3 turns to LOW level, and asdescribed above, the switch SW1 selects the constant voltage Vreg. Thus,an output current Io is obtained that is similar to that obtained whenthe PWM dimming signal S1 with an ON duty of 100% is fed to the outputcurrent controller 102. In this way, the light-emitting device shown inFIG. 1 can turn the light-emitting element Z1 ON irrespective of the PWMdimming signal S1 from the controller IC 200 when the controller IC 200is faulty.

Second Embodiment

FIG. 3 is a diagram showing a light-emitting device according to asecond embodiment. In FIG. 3, such parts as are found also in FIG. 1 areidentified by common reference numerals, and no detailed descriptionwill be repeated as to them.

The light-emitting device shown in FIG. 3 includes at least onelight-emitting element (in FIG. 3, light-emitting diodes) Z1, alight-emitting element driver IC 120 which drives the light-emittingelement Z1, a transistor P1 which is inserted in the power feed pathfrom the light-emitting element driver IC 120 to the light-emittingelement Z1, a controller IC 200 which feeds the light-emitting elementdriver IC 120 with a PWM dimming signal S1, and a monitor IC 300 whichchecks for a fault in the controller IC 200.

In the light-emitting element driver IC 120, an output voltage generator101′ substitutes for the output voltage generator 101 in thelight-emitting element driver IC 110 shown in FIG. 1. The output voltagegenerator 101′ varies the set value of the output voltage Vo accordingto the monitoring result signal S3 fed to the external terminal T15.Specifically, when the monitoring result signal S3 is at HIGH level,that is, when no signal indicating a fault in the controller IC 200 isreceived, the output voltage generator 101′ keeps the set value of theoutput voltage Vo at a standard value. On the other hand, when themonitoring result signal S3 is at LOW level, that is, when a signalindicating a fault in the controller IC 200 is received, the outputvoltage generator 101′ keeps the set value of the output voltage Vo at avalue smaller than the standard value. Accordingly, also the value ofthe output current Io is then smaller than when the set value of theoutput voltage Vo equals the standard value.

FIG. 4 is a timing chart illustrating an example of the operation of thelight-emitting device shown in FIG. 3, and depicts, from top down, theclock signal S2, the monitoring result signal S3, the PWM dimming signalS1, and the output current Io.

When a fault in the controller IC 200 causes the clock signal S2 tocease to be generated (after time point t1 in FIG. 4), no pulses appearin the PWM dimming signal S1 any longer (see broken lines in the PWMdimming signal S1 shown in FIG. 4), and the ON duty of the PWM dimmingsignal S1 becomes zero. However, when a fault in the controller IC 200causes the clock signal S2 to cease to be generated (after time point t1in FIG. 4), the monitoring result signal S3 turns to LOW level, and asdescribed above, the switch SW1 selects the constant voltage Vreg, andin addition the output voltage generator 101′ turns the set value of theoutput voltage Vo to a value smaller than the standard value. Thus, anoutput current Io continues to be obtained with a smaller value thanwhen the controller IC 200 is not faulty. In this way, thelight-emitting device shown in FIG. 3 can turn the light-emittingelement Z1 ON irrespective of the PWM dimming signal S1 from thecontroller IC 200 when the controller IC 200 is faulty.

Moreover, the light-emitting device shown in FIG. 3 can keep the valueof the output current Io smaller when the controller IC 200 is faultythan when the controller IC 200 is not faulty.

When the controller IC 200 is faulty, the electric power source fromwhich the input voltage Vi is derived may be in danger of approachingdepletion. However, as described above, the light-emitting device shownin FIG. 3 makes the value of the output current Io smaller when thecontroller IC 200 is faulty, and this reduces electric power consumptionin the light-emitting device shown in FIG. 3 when the controller IC 200is faulty. In this way, it is possible to make the electric power sourcefrom which the input voltage Vi is derived less likely to deplete whenthe controller IC 200 is faulty.

When the controller IC 200 is faulty, as a result of the output currentIo continuing to be fed to the light-emitting element Z1, thelight-emitting element Z1 may break depending on its specifications.However, as described above, the light-emitting device shown in FIG. 3makes the value of the output current Io smaller when the controller IC200 is faulty, and this prevents the light-emitting element Z1 frombreaking.

Third Embodiment

FIG. 5 is a diagram showing a light-emitting device according to a thirdembodiment. In FIG. 5, such parts as are found also in FIG. 16 areidentified by common reference numerals, and no detailed descriptionwill be repeated as to them.

The light-emitting device shown in FIG. 5 includes at least onelight-emitting element (in FIG. 5, light-emitting diodes) Z1, alight-emitting element driver IC 130 which drives the light-emittingelement Z1, a coil L1, an output capacitor C1, a sense resistor Rs, acapacitor C2, a controller IC 200 which feeds the light-emitting elementdriver IC 130 with a PWM dimming signal S1, and a monitor IC 300 whichchecks for a fault in the controller IC 200.

The light-emitting element driver IC 130 is a semiconductor integratedcircuit device (a so-called LED driver IC) that has integrated into itN-channel MOS field-effect transistors 1H and 1L (hereinafter referredto as high-side and low-side transistors 1H and 1L respectively), ahigh-side driver 2H and a low-side driver 2L, a diode D1, a drivercontroller 3, an amplifier 4, and a switch SW1. The light-emittingelement driver IC 130 also has external terminals T1 to T7 forestablishing electrical connection with the outside.

Outside the light-emitting element driver IC 130, the external terminalT3 is connected to a terminal to which the input voltage Vi is applied.To the external terminal T1, the PWM dimming signal S1 is fed. Theexternal terminal T2 is connected to the first terminal of the coil L1.The second terminal of the coil L1 (i.e., the terminal to which theoutput voltage Vo is applied) is connected to the first terminal (anode)of the light-emitting element Z1. The second terminal (cathode) of thelight-emitting element Z1 is connected to the first terminal of thesense resistor Rs. The second terminal of the sense resistor Rs isconnected to a ground terminal. The first terminal of the outputcapacitor C1 is connected to the second terminal of the coil L1. Thesecond terminal of the output capacitor C1 is connected to the groundterminal. The external terminal T4 is connected to the ground terminal.The external terminal T5 is connected via the capacitor C2 to the firstterminal of the coil L1. The external terminal T6 is connected to thefirst terminal of the sense resistor Rs. To the external terminal T7,the monitoring result signal S3 is fed.

Inside the light-emitting element driver IC 130, the drain of thehigh-side transistor 1H is connected to the external terminal T3. Thesource of the high-side transistor 1H is connected to the externalterminal T2. The gate of the high-side transistor 1H is connected to theoutput terminal of the high-side driver 2H. The drain of the low-sidetransistor 1L is connected to the external terminal T2. The source ofthe low-side transistor 1L is connected to the external terminal T4. Thegate of the low-side transistor 1L is connected to the output terminalof the low-side driver 2L. Thus, the high-side and low-side transistors1H and 1L are connected in series between the terminal to which theinput voltage Vi is applied and the ground terminal, and the connectionnode between them (i.e., the terminal to which a switching voltage Vswis applied) is connected via the coil L1 to the output capacitor C1.

Based on an instruction from the driver controller 3, the high-sidedriver 2H generates a control signal GH for the high-side transistor 1H.The high-side transistor 1H is ON when the control signal GH is at HIGHlevel, and is OFF when the control signal GH is at LOW level. Based onan instruction from the driver controller 3, the low-side driver 2Lgenerates a control signal GL for the low-side transistor 1L. Thelow-side transistor 1L is ON when the control signal GL is at HIGHlevel, and is OFF when the control signal GL is at LOW level.

The diode D1 and the capacitor C2, which is externally fitted to thelight-emitting element driver IC 130, constitute a bootstrap circuit.The bootstrap circuit generates a boost voltage Vbst. The anode of thediode D1 is connected to a terminal to which the constant voltage Vregis applied. The cathode of the diode D1 is connected to the externalterminal T5.

The first power terminal of the high-side driver 2H and the first powerterminal of the driver controller 3 are connected to the externalterminal T5 (i.e., the terminal to which the boost voltage Vbst isapplied). The second power terminal of the high-side driver 2H isconnected to the external terminal T2 (i.e., the terminal to which theswitching voltage Vsw is applied). Thus, the control signal GH appliedto the gate of the high-side transistor 1H, when at HIGH level, equalsthe boost voltage Vbst and, when at LOW level, equals the switchingvoltage Vsw.

The first power terminal of the low-side driver 2L is connected to theterminal to which the constant voltage Vreg is applied. The second powerterminal of the low-side driver 2L is connected to the external terminalT4 (i.e., the terminal to which a ground voltage GND is applied). Thus,the control signal GL applied to the gate of the low-side transistor 1L,when at HIGH level, equals the constant voltage Vreg and, when at LOWlevel, equals the ground voltage GND.

The operation of the bootstrap circuit configured as described abovewill now be described. When the high-side transistor 1H is OFF and thelow-side transistor 1L is ON so that the switching voltage Vsw is at LOWlevel (GND), a current that passes from the constant voltage Vregapplication terminal via the diode D1 into the capacitor C2 charges thecapacitor C2. At this time, the boost voltage Vbst approximately equalsthe constant voltage Vreg (more precisely, the constant voltage Vregminus the forward voltage drop Vf across the diode D1, i.e., Vreg−Vf).

On the other hand, when, with the capacitor C2 charged, the high-sidetransistor 1H is turned ON and the low-side transistor 1L is turned OFFso that the switching voltage Vsw rises from LOW level (GND) to HIGHlevel (Vi), the boost voltage Vbst is raised to a value (Vi+Vreg) thatis higher than the HIGH level (Vi) of the switching voltage Vsw by thecharge voltage (approximately Vreg) across the capacitor C2. Applyingthis boost voltage Vbst to the first power terminal of the high-sidedriver 2H makes it possible to turn the high-side transistor 1H ON andOFF reliably.

The switch SW1 operates according to the monitoring result signal S3 fedto the external terminal T7. Specifically, when the monitoring resultsignal S3 is at HIGH level, that is, when no signal indicating a faultin the controller IC 200 is received, the switch SW1 selects the PWMdimming signal S1 fed to the external terminal T1 to feed it to thedriver controller 3. On the other hand, when the monitoring resultsignal S3 is at LOW level, that is, when a signal indicating a fault inthe controller IC 200 is received, the switch SW1 selects the terminalto which the constant voltage Vreg (a voltage corresponding to the HIGHlevel of the PWM dimming signal S1) is applied to feed it to the drivercontroller 3.

When fed with a HIGH-level PWM dimmer signal S1 from the switch SW1, thedriver controller 3 drives the high-side and low-side drivers 2H and 2Lso as to turn the high-side and low-side transistors 1H and 1L ON andOFF according to a feedback voltage Vfb. Also, when fed with theconstant voltage Vreg from the switch SW1, the driver controller 3drives the high-side and low-side drivers 2H and 2L so as to turn thehigh-side and low-side transistors 1H and 1L ON and OFF according to thefeedback voltage Vfb. By contrast, when fed with a LOW-level PWM dimmersignal S1 from the switch SW1, the driver controller 3 drives thehigh-side and low-side drivers 2H and 2L so as to stop the operation forgenerating the output voltage Vo.

The amplifier 4 generates the feedback voltage Vfb by amplifying thevoltage across the sense resistor Rs that is applied between thenon-inverting input terminal (+) and the inverting input terminal (−) ofthe amplifier 4. Accordingly, the feedback voltage Vfb is a voltagesignal that increases and decreases according to the output current Iothrough the sense resistor Rs.

The high-side and low-side transistors 1H and 1L, the high-side andlow-side drivers 2H and 2L, the driver controller 3, and the amplifier 4thus generate the output voltage Vo from the input voltage Vi such thatthe output current Io through the light-emitting element Z1 remainsequal to the target value during the ON period (HIGH-level period) ofthe PWM dimming signal S1, and stop the operation for generating theoutput voltage Vo during the OFF period of the PWM dimming signal S1.

The light-emitting element driver IC 130, the coil L1, the outputcapacitor C1, the sense resistor Rs, and the capacitor C2 serve both asan output voltage feeder which generates the output voltage Vo from theinput voltage Vi based on the PWM dimming signal S1 from the controllerIC 200 to feed the output voltage Vo to the light-emitting element Z1and as an emergency driver which, on receiving a signal indicating afault in the controller IC 200, turns the light-emitting element Z1 ONirrespective of the PWM dimming signal S1 from the controller IC 200.

The timing chart (FIG. 2) illustrating an example of the operation ofthe light-emitting device shown in FIG. 1 illustrates an example of theoperation of the light-emitting device shown in FIG. 5 as well, andtherefore no overlapping description will be repeated.

Fourth Embodiment

FIG. 6 is a diagram showing a light-emitting device according to afourth embodiment. In FIG. 6, such parts as are found also in FIG. 5 areidentified by common reference numerals, and no detailed descriptionwill be repeated as to them.

The light-emitting device shown in FIG. 6 includes at least onelight-emitting element (in FIG. 6, light-emitting diodes) Z1, alight-emitting element driver IC 130 which drives the light-emittingelement Z1, a coil L1, an output capacitor C1, sense resistors Rs andRs′, a switch SW2, a capacitor C2, a controller IC 200 which feeds thelight-emitting element driver IC 130 with a PWM dimming signal S1, and amonitor IC 300 which checks for a fault in the controller IC 200.

The sense resistor Rs' is inserted between the ground terminal and thesecond terminal of the sense resistor Rs, and the switch SW2 isconnected in parallel with the sense resistor Rs′. The switch SW2operates according to the monitoring result signal S3. Specifically,when the monitoring result signal S3 is at HIGH level, that is, when theswitch SW2 receives no signal indicating a fault in the controller IC200, the switch SW2 is ON so as to short-circuit across the senseresistor Rs′. On the other hand, when the monitoring result signal S3 isat LOW level, that is, when the switch SW2 receives a signal indicatinga fault in the controller IC 200, the switch SW2 is OFF so as not toshort-circuit across the sense resistor Rs′. Thus, when the switch SW2receives a signal indicating a fault in the controller IC 200, the gainof the feedback voltage Vfb with respect to the output current Io ishigher and hence the value of the output current Io is smaller than whenthe switch SW2 receives no signal indicating a fault in the controllerIC 200.

The timing chart (FIG. 4) illustrating an example of the operation ofthe light-emitting device shown in FIG. 3 illustrates an example of theoperation of the light-emitting device shown in FIG. 6 as well, andtherefore no overlapping description will be repeated.

Fifth Embodiment

FIG. 7 is a diagram showing a light-emitting device according to a fifthembodiment. In FIG. 7, such parts as are found also in FIG. 5 areidentified by common reference numerals, and no detailed descriptionwill be repeated as to them.

The light-emitting device shown in FIG. 7 includes at least onelight-emitting element (in FIG. 7, light-emitting diodes) Z1, alight-emitting element driver IC 140 which drives the light-emittingelement Z1, a coil L1, an output capacitor C1, a sense resistor Rs, acapacitor C2, a controller IC 200′ which feeds the light-emittingelement driver IC 140 with a PWM dimming signal S1, and a monitor IC 300which checks for a fault in the controller IC 200′.

The controller IC 200′ additionally includes an enable circuit 203 andan external terminal T24 as compared with the controller IC 200 shown inFIG. 5. The enable circuit 203 generates an enable signal S4 based onthe clock signal S2. From the external terminal T24, the enable signalS4 is output. In this example, the enable signal S4 is used to enablethe light-emitting element driver IC 140. A HIGH-level enable signal S4serves as a signal that enables the light-emitting element driver IC140, and a LOW-level enable signal S4 serves as a signal (disablesignal) that disables the light-emitting element driver IC 140.

In the light-emitting element driver IC 140, a driver controller 3′substitutes for the driver controller 3 in the light-emitting elementdriver IC 130 shown in FIG. 5, and a switch SW3 and an external terminalT8 are additionally provided. To the external terminal T8, the enablesignal S4 is fed. The switch S3 operates according to the monitoringresult signal S3 fed to the external terminal T7. Specifically, when themonitoring result signal S3 is at HIGH level, that is, when no signalindicating a fault in the controller IC 200′ is received, the switch SW3selects the enable signal S4 fed to the external terminal T8 to feed itto the driver controller 3′. On the other hand, when the monitoringresult signal S3 is at LOW level, that is, when a signal indicating afault in the controller IC 200′ is received, the switch SW3 selects theterminal to which the constant voltage Vreg (a voltage corresponding tothe HIGH level of the enable signal S4) is applied to feed it to thedriver controller 3′.

The switch SW1 operates according to the monitoring result signal S3 fedto the external terminal T7. Specifically, when the monitoring resultsignal S3 is at HIGH level, that is, when no signal indicating a faultin the controller IC 200′ is received, the switch SW1 selects the PWMdimming signal S1 fed to the external terminal T1 to feed it to thedriver controller 3′. On the other hand, when the monitoring resultsignal S3 is at LOW level, that is, when a signal indicating a fault inthe controller IC 200′ is received, the switch SW1 selects the terminalto which the constant voltage Vreg (a voltage corresponding to the HIGHlevel of the PWM dimming signal S1) is applied to feed it to the drivercontroller 3′.

The driver controller 3′ is enabled when fed with a HIGH-level enablesignal S4 or the constant voltage Vreg from the switch SW2, and isdisabled when fed with a LOW-level enable signal S4 from the switch SW2.

When enabled and fed with a HIGH-level PWM dimmer signal S1 from theswitch SW1, the driver controller 3′ drives the high-side and low-sidedrivers 2H and 2L so as to turn the high-side and low-side transistors1H and 1L ON and OFF according to the feedback voltage Vfb. Also, whenenabled and fed with the constant voltage Vreg from the switch SW1, thedriver controller 3′ drives the high-side and low-side drivers 2H and 2Lso as to turn the high-side and low-side transistors 1H and 1L ON andOFF according to the feedback voltage Vfb. By contrast, when enabled andfed with a LOW-level PWM dimmer signal S1 from the switch SW1, thedriver controller 3′ drives the high-side and low-side drivers 2H and 2Lso as to stop the operation for generating the output voltage Vo.

The light-emitting element driver IC 140, the coil L1, the outputcapacitor C1, the sense resistor Rs, and the capacitor C2 serve both asan output voltage feeder which generates the output voltage Vo from theinput voltage Vi based on the PWM dimming signal S1 and the enablesignal S4 from the controller IC 200′ to feed the output voltage Vo tothe light-emitting element Z1 and as an emergency driver which, onreceiving a signal indicating a fault in the controller IC 200′, turnsthe light-emitting element Z1 ON irrespective of the PWM dimming signalS1 and the enable signal S4 from the controller IC 200′.

FIG. 8 is a timing chart illustrating an example of the operation of thelight-emitting device shown in FIG. 7, and depicts, from top down, theclock signal S2, the monitoring result signal S3, the PWM dimming signalS1, the enable signal S4, and the output current Io.

When a fault in the controller IC 200′ causes the clock signal S2 tocease to be generated (after time point t1 in FIG. 8), no pulses appearin the PWM dimming signal S1 any longer (see broken lines in the PWMdimming signal S1 shown in FIG. 8), with the result that the ON duty ofthe PWM dimming signal S1 becomes zero and the enable signal S4 falls toLOW level (see broken lines in the enable signal S4 shown in FIG. 8).However, when a fault in the controller IC 200′ causes the clock signalS2 to cease to be generated (after time point t1 in FIG. 8), themonitoring result signal S3 turns to LOW level, and as described above,the switches SW1 and SW3 both select the constant voltage Vreg. Thus, anoutput current Io is obtained that is similar to that obtained when thePWM dimming signal S1 with an ON duty of 100% is fed along with aHIGH-level enable signal S4 to the driver controller 3′. In this way,the light-emitting device shown in FIG. 7 can turn the light-emittingelement Z1 ON irrespective of the PWM dimming signal S1 and the enablesignal S4 from the controller IC 200′ when the controller IC 200′ isfaulty.

Sixth Embodiment

FIG. 9 is a diagram showing a light-emitting device according to a sixthembodiment. In FIG. 9, such parts as are found also in FIG. 7 areidentified by common reference numerals, and no detailed descriptionwill be repeated as to them.

The light-emitting device shown in FIG. 9 includes a plurality oflight-emitting elements (in FIG. 9, light-emitting diodes) Z1, alight-emitting element driver IC 150 which drives the light-emittingelements Z1, a coil L1, an output capacitor C1, a sense resistor Rs, acapacitor C2, a controller IC 200′ which feeds the light-emittingelement driver IC 150 with a PWM dimming signal S1 and feeds a voltagebooster IC 400 with an enable signal S4, a monitor IC 300 which checksfor a fault in the controller IC 200′, and a voltage booster IC 400which boosts the input voltage Vi to feed the boosted voltage to thelight-emitting element driver IC 150. In a case where the total forwardvoltage of a plurality of light-emitting elements Z1 is higher than theinput voltage Vi, a voltage boosting circuit (voltage booster IC 400) isprovided to boost the input voltage Vi as in this example. For example,in a case where the output voltage of a battery mounted on a vehicle isused as the input voltage Vi, the input voltage Vi can be so low thatthe total forward voltage of a plurality of light-emitting elements Z1tends to be higher than the input voltage Vi.

In the light-emitting element driver IC 150, as compared with thelight-emitting element driver IC 140 shown in FIG. 7, the switches SW1and SW3 and the external terminals T7 and T8 are omitted.

In this example, the enable signal S4 is used to enable the voltagebooster IC 400. A HIGH-level enable signal S4 serves as a signal thatenables the voltage booster IC 400, and a LOW-level enable signal S4serves as a signal (disable signal) that disables the voltage booster IC400.

The voltage booster IC 400 has external terminals T41 to T43. To theexternal terminal T41, the input voltage Vi is applied. When the voltagebooster IC 400 is enabled, a voltage that results from boosting theinput voltage Vi is output from the external terminal T42 to be fed tothe external terminal T3 of the light-emitting element driver IC 150 andto the first terminal of a switch SW4. The second terminal of the switchSW4 is connected via a resistor R1 to the connection node between thecathode of a first light-emitting element 5 among the plurality oflight-emitting elements Z1 and the anode of a second light-emittingelement 6 among the plurality of light-emitting elements Z1. The switchSW4 operates according to the monitoring result signal S3. Specifically,when the monitoring result signal S3 is at HIGH level, that is, when theswitch SW4 receives no signal indicating a fault in the controller IC200′, the switch SW4 is OFF. On the other hand, when the monitoringresult signal S3 is at LOW level, that is, when the switch SW4 receivesa signal indicating a fault in the controller IC 200′, the switch SW4 isON, so that part of the plurality of light-emitting elements Z1 (thesecond light-emitting element 6 and those light-emitting elements whichare provided on the cathode side of the second light-emitting element 6)turn ON. The current Isw4 through the switch SW4 is limited by theresistor R1. In this way, it is possible to prevent part of theplurality of light-emitting elements Z1 (the second light-emittingelement 6 and those light-emitting elements which are provided on thecathode side of the second light-emitting element 6) from being brokenby the current Isw4.

The voltage booster IC 400, the light-emitting element driver IC 150,the coil L1, the output capacitor C1, the sense resistor Rs, and thecapacitor C2 serve as an output voltage feeder which generates theoutput voltage Vo from the input voltage Vi based on the PWM dimmingsignal S1 from the controller IC 200′ to feed the output voltage Vo tothe light-emitting elements Z1. On the other hand, the voltage boosterIC 400, the switch SW4, and the resistor R1 serve as an emergency driverwhich, on receiving a signal indicating a fault in the controller IC200′, turns part of the plurality of light-emitting elements Z1 ONirrespective of the PWM dimming signal S1 from the controller IC 200′.Thus, the output voltage feeder and the emergency driver share thevoltage booster IC 400 between them.

FIG. 10 is a timing chart illustrating an example of the operation ofthe light-emitting device shown in FIG. 9, and depicts, from top down,the clock signal S2, the monitoring result signal S3, the PWM dimmingsignal S1, the enable signal S4, the output current Io, and the currentIsw4 through the switch SW4.

When a fault in the controller IC 200′ causes the clock signal S2 tocease to be generated (after time point t1 in FIG. 10), no pulses appearin the PWM dimming signal S1 any longer (see broken lines in the PWMdimming signal S1 shown in FIG. 10), with the result that the ON duty ofthe PWM dimming signal S1 becomes zero and the enable signal S4 falls toLOW level (see broken lines in the enable signal S4 shown in FIG. 10).However, when a fault in the controller IC 200′ causes the clock signalS2 to cease to be generated (after time point t1 in FIG. 10), themonitoring result signal S3 turns to LOW level, and as described above,the switch SW4 turns ON; thus, a current Isw4 passes through part of thelight-emitting elements Z1 so that this part of the light-emittingelements Z1 turn ON. In this way, the light-emitting device shown inFIG. 9 can turn some of the light-emitting elements Z1 ON irrespectiveof the PWM dimming signal S1 and the enable signal S4 from thecontroller IC 200′ when the controller IC 200′ is faulty.

<Application>

The light-emitting devices according to the embodiments described abovecan be suitably used as various lights on vehicles as shown in FIGS. 11and 12, such as head lights (including high-beam lamps, low-beam lamps,small lamps, fog lamps, and the like as necessary) X11, light sourcesfor daytime running lights (DRLs) X12, tail lamps (including smalllamps, back lamps, and the like as necessary) X13, stop lamps X14, andturn lamps X15.

A light-emitting element driver IC 11A may be provided as a module (likean LED head light module Y10 as shown in FIG. 13, an LED turn lampmodule Y20 as shown in FIG. 14, or an LED rear lamp module Y30 as shownin FIG. 15) in which it is incorporated along with externally fittedcomponents (such as an output capacitor C1, a capacitor C2, a coil L1, asense resistor Rs, etc.) and a light-emitting element Z1 as the drivingtarget, or may be provided as an IC by itself (like the light-emittingelement driver ICs 110 to 150) that is a half-finished productindependent of externally fitted components (such as an output capacitorC1, a capacitor C2, coil L1, a sense resistor Rs, etc.) and alight-emitting element Z1 as the driving target.

<Other Modifications>

Although the embodiments described above deal with configurations wherelight-emitting diodes are used as light-emitting elements, this is notmeant to limit how the invention should be implemented. Instead, forexample, organic electroluminescence elements may be used aslight-emitting elements.

The various technical features disclosed herein may be implemented inany other manners than as in the embodiments described above, and allowfor any modifications within the spirit of the technical ingenuityinvolved. For example, bipolar transistors and MOS field-effecttransistors can be substituted for each other as necessary, and thelogic levels of various signals can be inverted as necessary. Foranother example, the fifth and sixth embodiments can be modified to omitthe dimming function. That is, the embodiments described above should beconsidered to be in every aspect illustrative and not restrictive, andit should be understood that the technical scope of the presentinvention is defined not by the description of embodiments given abovebut by the appended claims and encompasses any modifications made in thesense and scope equivalent to those of the claims.

LIST OF REFERENCE SIGNS

-   -   1H N-channel MOS field-effect transistor (high-side transistor)    -   1L N-channel MOS field-effect transistor (low-side transistor)    -   2H high-side driver    -   2L low-side driver    -   3 controller    -   4 amplifier    -   5 first light-emitting element    -   6 second light-emitting element    -   110, 120, 130, 140, 150 light-emitting element driver IC    -   101 output voltage generator    -   102 output current controller    -   200, 200′ controller IC    -   201 clock circuit    -   202 PWM circuit    -   203 enable circuit    -   300 monitor IC    -   400 voltage booster IC    -   C1 output capacitor    -   C2 capacitor    -   D1 diode    -   L1 coil    -   P1 P-channel MOS field-effect transistor    -   R1 resistor    -   Rs, Rs' sense resistor    -   SW1-SW4 switch    -   T1-T8, T11-T15 external terminal    -   T21-T24, T31, T32, T41-T43 external terminal    -   X10 vehicle    -   X11 head light    -   X12 light source for daytime running light (DRL)    -   X13 tail lamp    -   X14 stop lamp    -   X15 turn lamp    -   Y10 LED head light module    -   Y20 LED turn lamp module    -   Y30 LED rear lamp module    -   Z1 light-emitting element (light-emitting diode)

1. A light-emitting element driving device for generating an outputvoltage from an input voltage based on a control signal from acontroller and feeding the output voltage to at least one light-emittingelement, the light-emitting element driving device comprising: a firsttransistor provided between a terminal to which the input voltage isapplied and a ground terminal; a first driver configured to generate afirst drive control signal for the first transistor; and a drivercontroller configured to drive the first driver according to a feedbackvoltage commensurate with a current passing in the at least onelight-emitting element and drive the first driver, when a first signalis input, such that the at least one light-emitting element is all orpartly turned ON irrespective of the control signal.
 2. Thelight-emitting element driving device according to claim 1, furthercomprising an amplifier configured to generate the feedback voltage. 3.The light-emitting element driving device according to claim 1, furthercomprising an input terminal to which the input voltage is applied. 4.The light-emitting element driving device according to claim 3, whereinthe first transistor is connected to the input terminal.
 5. Thelight-emitting element driving device according to claim 1, furthercomprising a terminal to which a cathode voltage of the at least onelight-emitting element is applied.
 6. The light-emitting element drivingdevice according to claim 1, further comprising a terminal via which thecontrol signal is input.
 7. The light-emitting element driving deviceaccording to claim 1, further comprising a terminal via which the firstsignal is input.
 8. The light-emitting element driving device accordingto claim 1, wherein the first signal is a signal that indicates anabnormality of the controller.
 9. The light-emitting element drivingdevice according to claim 1, further comprising: a second transistorprovided between the first transistor and the ground terminal; and asecond driver configured to generate a second drive control signal forthe second transistor.
 10. The light-emitting element driving deviceaccording to claim 1, wherein the driver controller is configured todrive the first driver, when the first signal is input, such that the atleast one light-emitting element is all or partly turned ON with apredetermined luminance irrespective of the control signal.
 11. Thelight-emitting element driving device according to claim 1, wherein thedriver controller includes a selector configured to select either thecontrol signal or a constant voltage.
 12. The light-emitting elementdriving device according to claim 11, wherein the selector is configuredto select the control signal when the first signal is not input andselect the constant voltage when the first signal is input.
 13. Thelight-emitting element driving device according to claim 1, furthercomprising an output terminal via which the output voltage is output,wherein an output capacitor is connected via a coil to the outputterminal.
 14. A light-emitting device comprising: the light-emittingelement driving device according to claim 1; and at least onelight-emitting element driven by the light-emitting element drivingdevice.
 15. The light-emitting device of claim 14, wherein thelight-emitting device is used as a vehicle-mounted lamp.
 16. A vehiclecomprising the light-emitting device of claim 15.